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METHYL ALCOHOL                            67
Properties.—Colourless liquid with a distinctive smell; b.p.
21° ; sp. gr. 0*807 at o° ; soluble in water, alcohol and ether.
Reactions.—Acetaldehyde and many of the aliphatic aldehydes
are characterised by the following reactions :—
1.  Prepare a little ammonio-silver nitrate by adding dilute
ammonia drop by drop to silver nitrate solution • until the pre-
cipitate just dissolves.   Add to a third of a test-tube full of the
ammonia-silver nitrate solution about i c.c. of aldehyde,, and
place it in a beaker of hot water.   A mirror of metallic silver is
deposited.    Ag2O + C2H4O = Ag2 + C2H4O2 (acetic acid).
2.  To i c.c. of aldehyde add 2-3 times its volume of a cold
saturated solution of sodium bisulphite and shake up.     The
additive compound,   CH3CH.OH.SO3Na, crystallises  out   on
standing.   A crystal of the substance introduced into the liquid
will hasten its formation.    The bisulphite solution is prepared
either by dissolving sodium metabisulphite   in water, or by
passing sulphur dioxide into soda crystals covered with a layer
of water.    It forms an apple-green solution, smelling strongly
of sulphur dioxide. The sulphur dioxide is conveniently obtained
from a bottle of the liquid which can be purchased, or by dropping
concentrated sulphuric acid on to solid sodium sulphite.
3.  A solution of magenta decolourised by  sulphur  dioxide
becomes violet on the addition of a drop of aldehyde (Schiff;.
Prepare a weak solution of magenta by dissolving a crystal in
half a test-tube of water and bubbling in sulphur dioxide until
the colour disappears.    Now add a few drops of aldehyde.
4.  Boil a few drops  of aldehyde  with i—2 c.c. of caustic
potash   solution.    The   liquid  becomes   yellow and  a  brown
resinous precipitate is formed.
5.  Add a drop or two of concentrated sulphuric acid to I c.c.
of aldehyde.    The mixture becomes hot in consequence of the
aldehyde undergoing polymerisation to paraldehyde (C2H4O)3j
b.p.   124°, which separates as an oil  on adding water.     See
Appendix', p. 238.
Methyl Alcohol.    CH3.OH
Commercial methyl alcohol is obtained by purifying wood spirit.
It often contains a little acetone, which may be detected by the
iodoform reaction (see p. 50). It may, if necessary, be purified by
boiling it, using an upright condenser, with 3—4 per cent, of solid